Dynamic time division duplex (dtdd) access for satellite ran

ABSTRACT

A ground station communicates with a satellite having a field of view (FOV), the satellite directly communicating with user equipment (UE) over uplink signals and downlink signals. The ground station has a Dynamic Time Division Duplex (DTDD) controller configured to establish UE uplink time slots during which the UE sends UE uplink signals, the UE uplink time slots based on a unique delay for the UE, whereby UE uplink signals are received at the satellite during a same satellite uplink time slot. The controller avoids overlapping uplink and downlink signals being received at the satellite, as well as at the UE.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Patent Application No.17/867,488, filed Jul. 18, 2022, which claims the benefit of priority ofU.S. Provisional Patent Application No. 63/222,633 filed Jul. 16, 2021,the entire contents of which are relied upon and incorporated herein byreference in their entirety.

BACKGROUND

Radio access network (RAN) has two types: FDD (frequency divisionduplex) and TDD (time division duplex) are two spectrum usagetechniques, both forms of duplex, used in mobile or fixed wirelessbroadband links. It is essential to these links that transmission canoccur in both directions simultaneously so that data can flow downlink(DL) and uplink (UL) at the same time. TDD uses a single frequency bandfor both transmit and receive. TDD alternates the transmission andreception of station data over time. Time slots may be variable inlength.

The real advantage of TDD is that it only needs a single channel offrequency spectrum. Furthermore, no spectrum-wasteful guard bands orchannel separations are needed. The downside is that successfulimplementation of TDD needs a very precise timing and synchronizationsystem at both the transmitter and receiver to make sure time slots donot overlap or otherwise interfere with one another.

SUMMARY

A ground station communicates with a satellite having a field of view(FOV), the satellite directly communicating with user equipment (UE)over uplink signals and downlink signals. The base station has a DynamicTime Division Duplex (DTDD) controller configured to establish UE uplinktime slots during which the UE sends UE uplink signals, the UE uplinktime slots based on a unique delay for the UE, whereby UE uplink signalsare received at the satellite during a same satellite uplink time slot.The controller avoids overlapping uplink and downlink signals beingreceived at the satellite, as well as at the UE.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram that shows a TDD channel applied to satellitecommunications;

FIG. 2(a) is a diagram showing TDD over satellite and supporting groundinfrastructure for a single satellite embodiment;

FIG. 2(b) shows TDD over satellite and supporting ground infrastructurefor a multiple satellite embodiment;

FIG. 2(c) is a flow diagram;

FIG. 3 is a diagram showing TDD Tx/Rx rings;

FIGS. 4(a), 4(b) are diagrams showing TDD channel using satellite;

FIG. 5(a) is a timing diagram for a GateWay Station (GWS), a singlesatellite (SAT) and UEs located in rings of FIG. 3 ;

FIG. 5(b) is a timing diagram for a GateWay Station (GWS), twosatellites (SAT1, SAT2) and UEs located in rings of FIG. 3 ; and FIG. 6is a diagram showing the Tx/Rx frequency split.

DETAILED DESCRIPTION

In describing the illustrative, non-limiting embodiments illustrated inthe drawings, specific terminology will be resorted to for the sake ofclarity. However, the disclosure is not intended to be limited to thespecific terms so selected, and it is to be understood that eachspecific term includes all technical equivalents that operate in similarmanner to accomplish a similar purpose. Several embodiments aredescribed for illustrative purposes, it being understood that thedescription and claims are not limited to the illustrated embodimentsand other embodiments not specifically shown in the drawings may also bewithin the scope of this disclosure. For example, “gNodeB” illustrationsand texts are equally applicable to eNodeB.

FIG. 1 shows a standard LTE (Long-Term Evolution) TDD frame of 10 ms. Asillustrated, the satellite has predetermined time slots during which anuplink signal is received and predetermined time slots during which adownlink signal is transmitted. In the example embodiment shown, theuplink and downlink time slots alternate with one another. At the groundstation processing device, such as an eNodeB, a 10 ms TDD frame has tensubframes 0-9. In the example embodiment shown, the first subframe 0 iswhen the eNodeB transmit a downlink signal to the UE via the satellite.That is followed by a second subframe, which is a special subframehaving a Downlink Pilot Time Slot (DwPTS), a Guard Pilot (GP) and anUplink Pilot Time Slot (UpPTS). That is followed by two Uplink subframes2, 3, during which the UE transmits an uplink signal to eNodeB at theground station, and then two Downlink subframes 4, 5, another specialsubframes, then another two uplink subframes 7, 8, and then a downlinksubframe 9 and the next subframe 0 of the next frame, just like thesubframe 0 of this frame at the beginning. Such cycle repeats to delivercontinuous DL and UL communications. There can be a few different ratioand granularity of DL and UL slots by RAN system configurations.

As further illustrated in FIG. 1 , the User Equipment (UE) on earthcommunicate with the eNodeB. Here, the UE initially receives a signalfrom the eNodeB during subframe 0, and receives a control signal duringthe DwPTS half-subframe, then transmits a signal during the UpPTShalf-subframe. The UE then switches to transmit during the subframes 2,3 for the Uplink signals. The DwPTS and UpPTS provide time to allowdownlink/uplink switching to be performed. When the UE switches back toreceive during the Downlink signal, it accounts for a Timing Advance(TA) (e.g., 20 μs). The eNodeB instructs the UE to transmit a bit earlyto meet the time slot at the eNodeB and avoid overlapping signals at theeNodeB. And, there is some offset between the satellite and the eNodeBto allow for switching from downlink to uplink and from uplink todownlink.

TDD is more flexible and efficient in spectrum usage, as the DL and ULtraffic is asymmetric and dynamically changing. NR Mid band and Highband only have TDD, and FDD stays only for Low band (FR1: below 6 GHz).It can work better than FDD, as the same frequency for Tx and Rx thereis no switch insertion loss. The TDD D/U ratio can be dynamicallyadjusted to suit for the needs, especially for wider bandwidth (BW). Thefuture will have more TDD for UE HW and e/gNB TR/Rx is simpler than FDD,the spectrum usage is more efficient.

Timing is often synched to precise GPS-derived atomic clock standards.Guard times are also needed between time slots to prevent overlap. Thistime is generally equal to the send-receive turnaround time(transmit-receive switching time) and any transmission delays (latency)over the communications path.

FIG. 2(a) shows a Dynamic Time Division Duplex (DTDD) access system andmethod according to the present disclosure. The DTDD system 100 includesa gateway 150 that communicates with one or more Low Earth Orbit (LEO)satellites 20 over Transmit and Receive beams Tx/Rx 12. The satellite 20directly communicates with one or more User Equipment (UE) 10 located incells 7 on earth over respective Transmit and Receive beams Tx/Rx 14.The gateway 150 has a gateway antenna 152, a gateway site 154, a firstprocessing device 156 a, a second processing device 156 b, and a DTDDcontroller 160. In the embodiment shown, the first processing device 156a includes one or more gNodeBs or eNodeBs, each to controlcommunications over beams 12, 14 with a first cell 7, and the secondprocessing device 156 b includes one or more gNodeBs, each to controlcommunications over beams 12, 14 with a second cell 7.

In FIG. 2(a), a single satellite 20 is utilized to communicate with UEs10 over different frequencies. Time slots are used for transmit signalsTx and receive signals Rx. The DTDD controller 160 separates thetransmit signal Tx and receive signal Rx in different frequencies. TheDTDD controller 160 dynamically controls operation of the system 100 tocoordinate communication between the satellite 20 and the ground station150 via the antennas 152, and the direct communication between thesatellite 20 and the UEs 10. The controller 160 controls the frequencyand timing amongst all of the UEs communicating on all of the pluralityof gNodeBs 156 to avoid any overlap of communication at the satellite20. The controller 160 can also receive information on the orbit, Fieldof View (FOV), etc., and control communications based on thatinformation. The controller 160 handles the frequency and time DL and ULsignals with their cell IDs to the plurality of gNodeBs 156, which thenprovide the synchronization and time slot assignment as normal. Thatinformation is then transmitted to and received by the UEs 10 via thesatellite 20, to control operation of the UEs to communicate on thedesignated frequencies and time resource allocations.

FIG. 2(b) is an example of another embodiment of the disclosureutilizing multiple satellites, a first satellite 20 a and a secondsatellite 20 b. However, additional satellites can be utilized, as aparticular cell 7 may be in communication with four or more satellitesat any given time. As illustrated, the first satellite 20 a communicatesa feeder link signal with the GW site 154 over a first beam 12 and thefirst satellite 20 a directly transmits downlink signals to the UEs onearth over a second beam 14. And the second satellite 20 b communicatesa signal with the GW site 154 over a third beam 13 and directly receivesuplink signals from the UE on earth over a fourth beam 16. And, asfurther shown, the second satellite 20 b can transmit a downlink signalto different cells than the downlink signal 14 from the first satellite20 a.

As the satellites orbit, the setting satellite 20 a can conduct handoverto transfer the uplink signal, then the downlink signal, for the cellsto the setting satellite 20 b; thus, when the second satellite 20 btakes over the uplink signal, then 20 a can release. However, in theembodiment shown, one satellite (the first satellite 20 a) communicatesthe downlink signal and a different satellite (the second satellite 20b) communicates the uplink signal; though in other embodiments a singlesatellite can conduct both uplink and downlink (FIG. 2(a)). In someembodiments, the transmit signal Tx is over a first frequency, and thereceive signal Rx is over a second frequency different than the firstfrequency for different regions/cells, while the Tx and Rx of the samefrequency from the same cell are handled separately by two satellites sothat with multiple satellites, TDD TRx collision can be avoidedcompletely, and the GWS 154 can route the TRx signal to two satellitesover different feeder links and combine the relevant DL and UL signalfor the BBUs, and the UEs can communicate uplink signals and downlinksignals as they do normally without causing timing collision issue onthe same satellite, as two satellites are handling Tx and Rx atdifferent position in the space. They have their own Tx and Rx beams forthe same cell. It is the ground gateway site managing the feeder linksand take the spatial diversity to resolve such challenges.

Accordingly, at any given time, the DTDD 160 dynamically controls theoperation of the system 100 in real time to coordinate communicationsbetween the first and second satellites 20 a, 20 b with the groundstation 150 over the antennas 152, and between the first and secondsatellites 20 a, 20 b directly with the UEs 7. The controller 160 canalso receive information on the orbit, Field of View (FOV), etc., andcontrol communications based on that information. The UEs 7 directlytransmit signals to the second satellite 20 b at a certain timesubchannel and receive signals from the first satellite 20 a at acertain time channel, so that there is no interference or overlap ofcommunications at the satellites 20 a, 20 b, and the satellites 20 a,are fully utilized.

Referring to the time vs. distance chart of FIG. 2(b), the FOV aregenerally large enough to find cells using LB or HB, so two satellitescan be arranged for taking care of two different bands, for example, 20a Tx LB cells, but Rx the HB cells; while 20 b Tx HB cells, but Rx theLB cells. In this way they can avoid TDD collision effectively.

FIG. 2(c) shows the operation 200 of the DTDD 160 in accordance with oneexample embodiment of the present disclosure. Starting at step 202, thesatellite control center provides information about the system,including for example the cells, RAT, frequencies, satellite(s) and gateway site. At step 204, the satellite control center also provides theTDD low band (Tx) cells and high band (Rx) cells and visible satellites20 by each and every cell 7. And, step 206, the satellite control centeralso provides the field of view for each satellite 20 when serving acell 7. The information from steps 202, 204, 206 can be accessed by orcommunicated to any of the DTDD 160 or the gNodeB.

At step 208, the DTDD 160 determines, for the information obtained fromthe NCC and the satellite control center, the best satellite transmitsignal Tx and satellite receive signal Rx for each cell. At step 210,the DTDD 160 allocates a frequency and time resource for each cell, step210. The controller 160 also determines (with respect to twosatellites), step 212, the routing arrangement of the feeder links, aswell as the direct digital control (DDC) parameters and, step 214, therouting arrangement (mapping) for satellite hand over. It then updatesthe satellite's position and field of view at the satellite controlcenter, step 216. That information is then transmitted to the UEs viathe gNodeBs and satellite(s). The gNodeB operates in accordance with itsstandard compliant procedures, and here configures the signal to abaseband signal for communication with the satellite(s). Thus, the DTDDcontroller 160 determines the frequency and time resource allocation foreach cell, step 210, and utilizes that information to configureoperation of the UL and DL signals at the satellite(s), UEs, and gateway station 154.

The entire operation at the DTDD 160 (as well as the satellite controlcenter) is conducted automatically and without any manual interaction.Accordingly, unless indicated otherwise the process can occursubstantially in real-time without any delay or manual action.

FIG. 3 is a diagram showing a FOV for a single satellite 20. The gNodeBs156 each separate the FOV into a plurality of concentric TDD Tx/Rx rings5 based on a distance (pathlength) from the satellite 20 to the ground.The shortest pathlength is at the center of the FOV at the first ring 5a, which is located directly below the satellite 20. Each subsequentsurrounding ring 5 b-5 g extends further outward from the first ring 5 aand is associated with a further distance from the satellite 20. Thesatellite 20 directly communicates with the UEs 7 positioned in each ofthe rings 5 a-5 g via a respective transmit beam 14 a-14 g and arespective receive beam 16 a-16 g.

The outermost ring 7 g is furthest from the satellite 20 and defines theouter perimeter of the FOV for the satellite 20. The beams 14 g, 16 gcommunicating with the outermost ring 7 g typically form an angle ofabout 20 degrees (though larger or smaller angles can be utilized) fromthe UEs 7 on the ground to the satellite 20. The FOV and rings 5 followthe satellite 20 as it orbits earth. One or more cells 7 a-7 g arelocated in a respective ring. For synchronization, area is in rings sothe latency to the satellite 20 is similar for all the UEs in each ring,and all the cells 7 in the FOV have the same ratio for DL/UL.

The beams 14, 16 track the cells and hence the cell tracking beamschange their rings every few seconds, which means the gNBs 156 shift thespecial time slot from one subframe to the next, so that all the FOVwould roughly align the TRx switching time on the same subframe. Suchdynamic changes are actually changing slowly and UEs are able to adaptto the changes. There are points where the special subframe need toshift when they are close to 1 ms drift due to satellites orbiting athigh speed, so that the changes match the protocol periodicity and thesmooth shifts of Tx-Rx time. Must follow the 1 ms granularity for thering sliding over the fixed cell. The Network Control Center (NCC),which is at the gate way site 154, and the NCC has a controller thatguides the ring switching for each Base Band Unit (BBU) of the gNodeB156, as well as handling communications at the satellites 20 a, 20 b foreach cell 7 (e.g., the operating parameters for the Tx/Rx beams of thecell 7). Each gNodeB 156 can have a plurality of BBUs, each of which hasa controller that controls a single cell 7.

The solution for better use of the TDD spectrum resources by havingdifferent DL/UL ratio (the respective number of DL and UL subframe)would be a new use of TDD bandwidth part (BWP) in smaller granularity(say 20 MHz) into multiple TDD BWPs (4×5 MHz) and do the different DL/ULratio for each partition of BWs, so that there will be differentfrequency sub-band usage by all the cells to avoid phase array Rx sufferfrom interference of the strong Tx. Dynamic adjusting of the TDDresources according to the needs as shown in FIG. 6 . Thus, within theTDD, each BWP can have a different frequency. For example, any overlapin DL and UL processing can be resolved by assigning a differentfrequency for the DL and UL signals.

The width of each ring 5 can be smaller with HB (high band, i.e.,approximately 2 GHz), as the cell size reduces, hence ring changingwould be quicker than LB (low band, approximately 1 GHz), but a fewseconds for a ring change is not too much for a gNodeB. Scheduling isparameterized with any ring.

One objective of the above description is to be able to run the TDD witha modified gNodeB but minimizing additional changes. Running an enginethat can recover the frequency dimension lost when working on TDDinstead of FDD. The DTDD controller 160 provides a dynamic and real-timeassignment of the frequencies depending on the position on the ring 5and makes the operation transparent to the gNodeB 156 and the UE 10.

It cross-correlates and assigns in real-time the frequency plan, witheach carrier assigned to either to Tx or Rx; there is a scheduler thatdetermines the best means of transmitting each carrier in real time,using carrier planning that continuously adjusting itself in real time.Each carrier is assigned just for Tx or Rx and they're assigned indifferent ring levels to minimize the delay difference impact.

Turning to FIG. 4(a), a timing diagram is shown to illustrate an issuewith TDD when used for a single satellite having ten frames 0-9. Adownlink signal is transmitted from the satellite 20 to the UE 10, whichis transmitted from the satellite 20 during a satellite downlink frameDL-SAT and received at the UE during a UE downlink frame DL-EU. Thedownlink signal starts at a first time period T=0, but due to thepathlength from the satellite 20 to the UE 10, there is a delay untilthe downlink signal is first received at the UE, at T=1. In addition, anuplink signal is transmitted from the UE to the satellite, which istransmitted from the UE during a UE uplink frame UL-EU and received atthe satellite during a satellite uplink frame UL-SAT.

That delay in transmission between the satellite and the UE causes anoverlap in operation when the satellite 20 changes from transmittingdata to the UEs 10 in the downlink frames, to receiving data from theUEs 10 in the uplink frames, as shown where the DL-UE and UL-UE overlapat T=5 to T=8. For example, the satellite 20 continues to transmit thedownlink signal until time T=6, and from T=7 to T=10 the satellite 20receives uplink data. In addition, at time T=5, the UE must begin totransmit data to the satellite 20 in order for that data to be receivedat the beginning of the uplink frames at T=7 to make full use of thesatellite and maximize satellite operations. Consequently, anytransmission from the satellite to the UE after a certain time, say T=6,will be received at the UE when the UE is in the transmission mode, atT=8. More specifically, the UE will both be receiving data from thesatellite and also transmitting data to the satellite from T=5 to T=8.That period of overlapping operation cannot be reliably performed by theUE and is likely to have errors and interference.

In FIG. 4(b) it is shown that the greater the distance in the FOVbetween the satellite and the UE, the greater the pathlength, and thelonger the delay in the UL and DL transmissions, which can be furtherbased on orbital position, FOV and other factors. Where the delay islong enough, it can resolve the overlapping operation at the UE; asshown, there is no overlap between the DL-UE frame and the UL-UE frame.However, a longer delay causes an overlapping operation at the satellite20 when the satellite converts from downlink during the DL-SAT frames touplink during the UL-SAT frames, which also is undesirable. Accordingly,a delay is needed that avoids overlapping operations at both the UE andthe satellite.

FIG. 5(a) shows a timing diagram for a single satellite operation (FIG.2(a)) to maximize capacity at the satellite 20, and FIG. 5(a) shows atiming diagram for two satellite operation (FIG. 2(b)) to maximizecapacity at the satellites 20 a, 20 b. Referring first to FIG. 5(a), thefigure shows an example where UEs 10 b, 10 d, 10 g are active in threeof the rings, namely rings 5 b, 5 d and 5 g, respectively. As shown, theUEs 10 b, 10 d, 10 g transmit respective signals on respectivedistinctive beams 16 b, 16 d, 16 g during respective uplink time framesUL-UEb, UL-UEd, UL-UEg to the satellite 20 to be processed at thesatellite 20 during an uplink frame UL-SAT from T=6 to T=7. For theuplink beams 16 b, 16 d, 16 g to be received at the same time T=6, theUE 10 g in the furthest ring 5 g must begin transmitting at the earliesttime T=0 to T=3, time frame UL-UEg, since that UE transmission has thelongest pathlength and the longest delay. The UE 10 d in the nextfurthest ring 5 d in the example must begin transmitting at the nextearliest time T=1 to T=4, time frame UL-UEd. And the UE 10 b in theclosest ring 5 b begins transmitting at the latest time T=2 to T=5, timeframe UL-UEb. Accordingly, the beams from each of the rings 5 g, 5 d, 5b arrive simultaneously at the satellite time slot UL-SAT at T=6 to T=7.

The satellite 20, also during the satellite uplink time frame UL-SAT,transmits the uplink signals 12 UL to the gate way site 154 and after adelay is received at T=8 to T=9 during an uplink time slot at the gateway site UL-GWS. At the next downlink time slot at the gate way siteDL-GWS, at time T=9 to T=10, the gate way site 154 transmits a downlinksignal 12DL to the satellite 20. It is received at the satellite duringa satellite downlink time slot DL-SAT from T=11 to T=12. Thus, the ULsubframe for the UEs in different rings are offset with respect to oneanother so that the UL signals are synchronized when received at thesatellite.

At that same time, the satellite simultaneously transmits that downlinksignal on respective distinctive downlink beams 14 b, 14 d, 14 g, allstarting at the same time T=11 and ending at the same time T=12. Theclosest UEs 10 b (i.e., the UEs in ring 5 b, FIG. 3 ) receives thedownlink signal 14 b first, at DL-UEb, because it has the least delay incommunication with the satellite based on its pathlength and otherfactors. The next closest UE 10 d (i.e., the UEs in ring 5 d, FIG. 3 )receives the signal 14 d next, at DL-UEd, and the furthest UE 10 g(i.e., the UEs in ring 5 g, FIG. 3 ) receives the downlink signal 14 glast, at DL-UEg. Thus, the DTDD controller 160 provides different delaysfor the UEs located in the various rings 5 a-5 g of FIG. 3 , to avoidoverlapping UL and DL frames at the GWS 154, the satellite 20, and/orthe UEs 10. That is, the UEs 10 located in the closest ring 5 a will allbe associated with a first delay, the UEs 10 located in the next closestring 5 b will all be associated with a second delay longer than thefirst delay, and the UEs located in the furthest ring 5 g will all beassociated with a seventh delay longer than the first-sixth delays forrings 5 a-5 f. Thus, the DL signal is synchronized at the satellite 20.

Accordingly, UE uplink frames for the three UEs, namely uplink framesUL-UEb, UL-UEd, UL-UEg, are offset with respect to one another, and canoverlap (or not) with one another. However, the UE closest to thesatellite, UEb, has an uplink frame UL-UEb that starts and ends last atT=2 to T=5 and a downlink frame DL-UEb that starts and ends first, atT=13 to T=16; the next closest UEd has an uplink frame UL-UEd thatstarts and ends after the closest UEb starts and ends, at T=1 to T=4,and a downlink frame DL-UEd that starts and ends after the closest UEbstarts and ends, at T=14 to T=18; and the furthest UEg has an uplinkframe UL-UEg that starts and ends last (after UL-UEb and UL-UEd startand end), at T=15 to T=18. The UE frames can be stretched to accommodatethat timing. However, for a single satellite (FIG. 2(a)), the TDD Txsignals may interfere with the Rx signals.

As further illustrated in FIG. 5(a), there is no overlapping operationat any of the gate way site 154, the satellite 20 or the UEs 10. Thatis, none of those elements need to receive and transmit at the sametime. And, communications occur without collision between transmit andreceive for all UEs 10 in all cells 7. And, the satellite uplink canstart and end at the same time, T=6 to T=7; and the satellite downlinkcan start and end at the same time, T=11 to T=12. That entire operationis coordinated by the DTDD controller 160.

Though FIG. 5(a) is illustrated for a single satellite (FIG. 2(a)) for aparticular case to avoid Tx Rx collision, such case is with constraintsof cell position, U/D periods matching the delay, it is clear that thenext frame will run into collision. So, with one satellite TDD ischallenging. However, the solution does exist when the fullconstellation of satellites are available, as in that case each cell cansee normally 4 satellites. Hence a better TDD solution can be formedfrom two satellites (FIG. 2(b)), one does the Tx only while the otherdoes the Rx, as shown for example in FIG. 5(b). The 3D diagram (FIG.2(b)) illustrates spatial, time and frequency diversity to avoid theinterference from Tx of 2 or 2+ satellites. The 2+ satellites handlingTDD case would be the preferred one as there is no restrictions on theDL and UL fractions, and can fit in the demand better.

Referring to FIG. 5(b), a timing diagram is shown where there are twosatellites (FIG. 2(b)), where a first satellite (SAT1) 20(a) onlyconducts uplink (U), and a second satellite (SAT2) 20(b) only conductsdownlink (D), for a given UE or cell or FOV. Thus, starting at a firsttime period, T=0 to T=1, all of the UEs from all of the rings 5 b, 5 d,5 g transmit an uplink signal 16 during its uplink frame, UL-UEb,UL-UEd, UL-UEg. Because the UEs are in different rings and at differentdistances from the second satellite 20(b), those signals arrive at thesecond satellite 20(b) at different times. Namely, the uplink signalfrom the closest UEb, UL-UEb arrives at a frame that starts and endsfirst, at times T=2 to T=4; the uplink signal from the next closest UEd,UL-UEd arrives at a frame that starts and ends after the first signalUL-UEb, at times T=3 to T=6; and the furthest UEg, UL-UEg arrives at aframe that starts and ends after the first and second signals, UL-UEband UL-UEb, at times T=5 to T=7.

The second satellite 20(b) operates as a pass through and sends thoseoffset signals to the gate way site 154. The DTDD 160 applies arespective delay to each signal. The signal 16 b from frame UL-UEbarrived first, so the DTDD applies the longest delay, Delay b. Thesecond signal 16 d to arrive is from UL-UEd, and the DTDD 160 gives thata Delay d, which is shorter than the first delay, Delay b. And the lastsignal 16 g to arrive is from frame UL-UEg, which receives the shortestdelay, Delay g. The delays b, d, g are configured so that all of theuplink signals are recognized at the DTDD 160 at a same time, startingat T=8 and ending at time T=9. Thus, although the signals 16 b, 16 d, 16g arrived at the second satellite 20(b) at different times, they are allsynchronized at the gate way 154, for example at the DTDD 160. It isnoted that although all the uplink signals 16 b, 16 d, 16 g are shownbeing sent at the same time (T=0 to T=1 in the example embodiment shown)from the UEs 10 b, 10 d, 10 g, they can be sent at different times andan appropriate delay can be applied to each respective signal by theDTDD 160. However, in some embodiments, the uplink signals from the UEsare all on the same band, and can be the same or different frequencies.The downlink signals 14 b, 14 d, 14 g can be treated in a similarmanner, with a delay being applied at the gate way such as by the DTDD160, so that the downlink signals are sent at different times (thoughshown in the figure at the same time), so they arrive at the UEs at asame time period.

One goal in FIGS. 2(a), 2(b), 5(a), 5(b) is to make the TRx switching onthe same subframe timing that can be achieved by each eNB to configurethe timeslots for downlink and uplink with and/or without frequencyscheduling resources according to the needs of the active UEs. Thus, theDL and UL do not occur at the same time, same distance and samefrequency.

Turning to FIG. 6 , another embodiment of the disclosure is illustrated.Here, the uplink and downlink signals can be on different frequencies toeliminate interference at the GWS 154, satellite 20 and/or UE 10, eitheron a same beam or different beams. FIG. 6 shows the Tx/Rx frequencysplit: the frequency dimension and Tx/Rx separation is recovered with anexternal controller. This is transparent for the gNodeB, but acoordinated mapping of the radio resources: 1 and 2 here are timeslotsfor smaller scale FDD within a TDD system in this context. The furtherintroduction of such FDD can avoid the interference between Tx and Rx,and can be very dynamic. In time collision case in a TDD case, usingdifferent sub carriers for Tx and Rx can help avoid interference.

The DTDD system 100 addresses two issues. First, Satcom RF path lengthdelay is much longer than the TDD DL and UL cycle (10 ms in general).Unlike FDD, where there is an extra dimension of frequency to make theTx and Rx independent of each other, and full duplex works gracefullywithout restriction to each other. The DTDD provides that extradimension back to the TDD link in a transparent way for the cellularsystem (gNodeB to UE connection).

Second, RF path length differences to the cells in the satellite FoVwould mean that the delay normalisation would make satellite beams TRxnot aligned between all the cells 7 in the FoV, and that would causesome cells that are transmitting Tx to interfere with the cells that arereceiving Rx. With the addition of the concept of rings (FIG. 3 ) thesynchronization is done in each of them, so the latency to the satelliteis similar for all the UEs in each ring.

In addition to the above solution, with full constellation, a cell wouldbe covered by more than one beam from different satellites, theoverlapping FOV can have the advantage of solving the above TDD Tx/Rxcollision on one satellite. The multiple satellites can do independentTx/Rx for each other and avoid collision 100% if coordinated well. Thereis no restriction with regards to the Tx and Rx switching time, as thereis only Tx or Rx for that band. The gNodeB needs to configure thescheduler and keep the same ratio of D/U on all the cells the satellite20 is serving. The gNodeB and/or DTDD controller 160 can handle Dopplercompensation for the UEs.

It is implemented at the gateway, outside the gNodeB. The flow chartshould have a transmission from gNodeB in frequency A, then a frequencyconversion to get to the satellite in V band, then another frequencyconversion to transmit in frequency B, within the same band but with anoffset. Then the UE will transmit back in frequency A, this will beconverted also to V band, and sent back to the gNodeB in frequency A.

It is noted that the FOV is divided into concentric rings or circles.However, any suitable separation can be provided.

In the embodiments disclosed, the DTDD controller 160 (as well as theBBU controller and the NCC controller) can include a processing deviceto perform various functions and operations in accordance with thedisclosure, though operation can alternatively be performed at thegNodeB 156 and/or the satellite 20. The processing device can be, forinstance, a computer, personal computer (PC), server or mainframecomputer, or more generally a computing device, processor, applicationspecific integrated circuits (ASIC), or controller. The processingdevice can be provided with one or more of a wide variety of componentsor subsystems including, for example, wired or wireless communicationlinks, input devices (such as touch screen, keyboard, mouse) for usercontrol or input, monitors for displaying information to the user,and/or storage device(s) such as memory, RAM, ROM, DVD, CD-ROM, analogor digital memory, flash drive, database, computer-readable media,floppy drives/disks, and/or hard drive/disks. All or parts of thesystem, processes, and/or data utilized in the system of the disclosurecan be stored on or read from the storage device(s). The storagedevice(s) can have stored thereon machine executable instructions forperforming the processes of the disclosure. The processing device canexecute software that can be stored on the storage device. Unlessindicated otherwise, the process is preferably implemented inautomatically by the processor substantially in real time without delay.In some embodiments, the system 100 of the present disclosure isconfigured to operate and communicate with standard UEs 10. That is, theUE can be a standard UE without any special electronic components oroperating software. In addition, the entire process is conductedautomatically by the processor, and without any manual interaction.Accordingly, unless indicated otherwise the process can occursubstantially in real-time without any delay or manual action.

The description and drawings of the present disclosure provided in thepaper should be considered as illustrative only of the principles of thedisclosure. The disclosure may be configured in a variety of ways and isnot intended to be limited by the preferred embodiment. Numerousapplications of the disclosure will readily occur to those skilled inthe art. Therefore, it is not desired to limit the disclosure to thespecific examples disclosed or the exact construction and operationshown and described. Rather, all suitable modifications and equivalentsmay be resorted to, falling within the scope of the disclosure.

1. A satellite communication system, comprising: a first satelliteconfigured for operative communication with a gateway device via a firstfeeder link and for direct communication with one or more user equipment(UE) over respective uplink signals and downlink signals, the firstsatellite having a first field of view (FOV) encompassing a firstplurality of cells; and a second satellite configured for operativecommunication with the gateway device via a second feeder link and fordirect communication with one or more UE over respective uplink signalsand downlink signals, the second satellite having a second FOVencompassing a second plurality of cells, a selected one of the secondplurality of cells corresponding to a selected one of the firstplurality of cells; wherein: the first satellite is configured toreceive, according to timing information received from the gatewaydevice via the first feeder link, an uplink signal during a first timeslot to a given one of the one or more UE located in the selected one ofthe first plurality of cells that corresponds to the selected one of thesecond plurality of cells; and the second satellite is configured totransmit, according to timing information received from the gatewaydevice via the second feeder link, a downlink signal to the given UEduring a second time slot that does not overlap with the first timeslot.
 2. The satellite communication system of claim 1, wherein: thefirst satellite is configured to receive the uplink signal over a firstfrequency; and the second satellite is configured to transmit thedownlink signal over a second frequency that does not overlap with thefirst frequency.
 3. The satellite communication system of claim 1,wherein: the first satellite is selected to only receive uplink signalsfrom the given UE within the selected cell; and the second satellite isselected to only transmit downlink signals to the given UE within theselected cell.
 4. The satellite communication system of claim 1, whereinthe first satellite and the second satellite are positioned to providespatial diversity with the selected cell, and the first satellite andthe second satellite communicate with the given UE within the selectedcell according to time diversity and frequency diversity.
 5. Thesatellite communication system of claim 1, wherein: the first satelliteis selected to only conduct uplink communication with the selected cell;and the second satellite is selected to only conduct downlinkcommunication with the selected cell.
 6. The satellite communicationsystem of claim 1, wherein: the first satellite is selected to onlyconduct uplink communication within the first FOV; and the secondsatellite is selected to only conduct downlink communication within thesecond FOV.
 7. The satellite communication system of claim 1, furthercomprising the gateway device.
 8. The satellite communication system ofclaim 7, wherein the gateway device includes a dynamic time divisionduplex (DTDD) controller configured to establish communication timeslotsfor use by the first and second satellites during communication with thegiven UE.
 9. The satellite communication system of claim 8, wherein thetimeslots are selected to have corresponding delays to avoid overlapbetween the uplink signal and the downlink signal.
 10. The satellitecommunication system of claim 8, wherein the DTDD controller isconfigured to determine a routing arrangement of the first and secondfeeder links.
 11. The satellite communication system of claim 10,wherein the DTDD controller is further configured to determine at leastone of direct digital control parameter or a mapping for satellitehandover between the first satellite and the second satellite.
 12. Thesatellite communication system of claim 7, wherein the gateway device isconfigured to segregate the at least one of the first FOV or the secondFOV into a plurality of concentric rings, each of the plurality ofconcentric rings having a corresponding delay for use with one or bothof the uplink signal and the downlink signal.
 13. The satellitecommunication system of claim 12, wherein: each concentric ringassociated with the first satellite corresponds to a differentpathlength from the first satellite to the Earth; and each concentricring associated with the second satellite corresponds to a differentpathlength from the second satellite to the Earth.
 14. A satellitecommunication system configured for communication with a satellitehaving a field of view (FOV), in which the satellite is configured todirectly communicate with user equipment (UE) over uplink signals anddownlink signals, the satellite communication system comprising: acontroller having one or more processors configured to: segregate theFOV of the satellite into a plurality of concentric rings, each of theplurality of concentric rings being associated with a respective delay;establish a first UE uplink time slot having a first delay for a firstone of the plurality of concentric rings, for transmission by a first UElocated within the first concentric ring; and establish a second UEuplink time slot having a second delay for a second one of the pluralityof concentric rings, for transmission by a second UE within the secondconcentric ring; wherein the first and second delays are established toavoid overlapping transmission between the first UE and the second UE.15. The satellite communication system of claim 14, wherein eachconcentric ring corresponds to different a pathlength from the satelliteto the Earth.
 16. The satellite communication system of claim 14,wherein an outermost one of the plurality of concentric rings defines anouter perimeter of the FOV of the satellite.
 17. The satellitecommunication system of claim 14, wherein the plurality of concentricrings follows the satellite as it orbits the Earth.
 18. The satellitecommunication system of claim 14, wherein a given one of the pluralityof rings encompasses a plurality of cells within the FOV.
 19. Thesatellite communication system of claim 14, wherein the controller isconfigured to adjust placement of at least one of a downlink pilot timeslot or an uplink pilot time slot within different communicationsubframes.
 20. The satellite communication system of claim 19, whereinthe adjustment is based on an orbiting speed of the satellite.
 21. Thesatellite communication system of claim 14, wherein the satellitecomprises a pair of satellites, and the controller is further configuredto cause each one of the pair of satellites to communicate directly withthe UE over distinct, nonoverlapping frequencies.